Phase doubling for switching power supply

ABSTRACT

A switching power supply control system may include logic to generate a greater number of second switching control signals in response to a first number of original switching control signals. For example, the logic may increase the number of phases that may be controlled by an existing switching power supply controller. The logic may be configured to steer feedback signals from the increased number of phases back to original feedback inputs on the controller.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/400,749, entitled Phase Doubling for Switching Power Supply, filedApr. 6, 2006, which claims priority to U.S. Provisional Application Ser.No. 60/714,657 entitled Method For Doubling Phases In A Switching PowerSupply, filed Sep. 6, 2005, which are incorporated by reference in theirentirety.

BACKGROUND

FIG. 1 illustrates a prior art switching power supply with outputcurrent sensing as disclosed in U.S. Pat. No. 6,683,441. The system ofFIG. 1 includes a controller 20 that generates switching control signalsSC1 and SC2 to drive switch circuits 10 and 12, thereby controlling theamount of power delivered to the load 22 through inductors 14 and 16.Additional circuitry would typically be included to sense the outputvoltage V_(OUT) so the controller can modulate the switch signals tomaintain a constant output voltage regardless of the amount of currentconsumed by the load. The sensed output voltage is usually combined withan input signal to generate an error signal that is applied to thecontroller for closed-loop control of the output. Additional componentssuch as capacitors would typically also be added for filtering theoutput voltage.

The system of FIG. 1 also includes a current sensing circuit 18 togenerate a signal V_(CS) that provides a measure of the total combinedoutput current delivered to the load. The current sense signal may beused in numerous ways. For example, it may be used to provideover-current shutdown, it may be used to implement current-moderegulation, or it may be combined with voltage feedback to establish adroop impedance for adaptive voltage positioning (AVP) control schemes.

The system of FIG. 1 is known as a multi-phase switching power supplybecause the power components including the switches and inductors arerepeated to produce multiple output currents that are summed together toprovide the total output current. This increases the amount of currentavailable from the power supply, but also increases the complexity ofthe controller and sensing circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art multi-phase switching power supply.

FIG. 2 illustrates an embodiment of a switching power supply controlsystem according to the inventive principles of this patent disclosure.

FIG. 3 illustrates another embodiment of a switching power supplycontrol system according to the inventive principles of this patentdisclosure.

FIG. 4 illustrates an example embodiment of a switching power supplycontrol system according to the inventive principles of this patentdisclosure.

FIG. 5 illustrates an example embodiment of a feedback network accordingto the inventive principles of this patent disclosure.

FIG. 6 illustrates a generalized embodiment of a switching power supplycontrol system according to the inventive principles of this patentdisclosure.

FIG. 7 illustrates example waveforms of signals for the embodiment ofFIG. 6.

FIG. 8 illustrates another example embodiment according to the inventiveprinciples of this patent disclosure.

FIGS. 9 and 10 illustrate example waveforms for embodiment of FIG. 8.

DETAILED DESCRIPTION

FIG. 2 illustrates an embodiment of a switching power supply controlsystem according to the inventive principles of this patent disclosure.The embodiment of FIG. 2 includes a controller 24 that may generate anynumber of first switching control signals SC1, SC2, etc., that areintended to control switches in a switching power supply. In thisexample, the number of first signals is one, but the inventiveprinciples of this patent disclosure apply to a controller having anynumber of switching control signals. Logic 26 uses the first switchingcontrol signals to generate a greater number of second switching controlsignals SCA, SCB, etc. In this example, there are two second signals.Thus, the embodiment of FIG. 2 may allow a controller that is designedfor a certain number of phases to control even more phases in aswitching power supply.

The logic 26 may be configured to generate the second switching controlsignals SCA, SCB, etc. in any desired sequence. For example, secondswitching control signals may be divided into sets with a first setcontrolled in a first sequence and a second set controlled in a secondsequence. If the first switching control signals SC1, SC2, etc. arecontrolled so that they are activated in a predetermined sequence, thesame sequence may be used for the first and second sets of the secondswitching control signals SCA, SCB, etc. For instance, the first set ofsecond signals may be activated in the predetermined sequence, followedby the second set being activated in the predetermined sequence. Thelogic may continue to alternate between activating first and second setsin the predetermined sequence or in any other desired sequence.

FIG. 3 illustrates another embodiment of a switching power supplycontrol system according to the inventive principles of this patentdisclosure. The embodiment of FIG. 3 includes a controller 28 and logic30 that operates in a similar manner to the embodiment of FIG. 2. Thelogic in the embodiment of FIG. 3, however, is configured to steer anumber of second feedback signals FBA, FBB, etc. to a lesser number offirst feedback signals FB1, FB2, etc. Steering may be accomplishedthrough various techniques, for example, a multiplexer using discreteswitches, resistive dividers connected to switching nodes, etc. In thisexample, the number of first feedback signals is one, and the number ofsecond feedback signals is two but the inventive principles are notlimited to any particular numbers. Each of the first feedback signalsmay be coordinated with a corresponding one of the first switchingcontrol signals. Likewise, each of the second feedback signals iscoordinated with a corresponding one of the second switching controlsignals. The embodiment of FIG. 3 may, for example, allow a controller28 that is designed for a certain number of phases to control even morephases in a switching power supply without affecting the feedbackcontrol loop of the system.

FIG. 4 illustrates an example embodiment of a switching power supplycontrol system that illustrates how the inventive principles of thispatent disclosure may be applied to double the number of phases that maybe controlled by an existing switching power supply controller. Thecontroller 32 illustrated in FIG. 4 may be, for example, a three-phasecontroller that implements a pulse width modulation (PWM) control schemeby driving three switches (or pairs of switches) with switching controlsignals PWM1, PWM2 and PWM3. A logic circuit includes six AND gates34A-34F that multiplex the original set of three control signalsPWM1-PWM3 into six control signals PWMA-PWMF. A D-type flip-flop 36 isclocked by PWM3 to enable a first set of three of the gates 34A-C whilea second set 34D-F is disabled during a complete sequence of PWM1-3. Theflip-flop then disables the first set while the second set is enabledduring another complete sequence of PWM1-3. Thus, the logic alternatesbetween activating PWMA-C and PWMD-F in the same sequence as theoriginal three switching control signals PWM1-3. The six switchingcontrol signals PWMA-F may be used to drive six switches (or pairs ofswitches) to implement a six-phase switching power supply.

FIG. 5 illustrates an example embodiment of a feedback network accordingto the inventive principles of this patent disclosure. The network ofFIG. 5 may be used, for example, in conjunction with the logic of FIG. 4to provide feedback from double the number of phases normallyimplemented by an existing switching power supply controller. In theembodiment of FIG. 4, an existing switching power supply controller 32that implements a three-phase PWM control scheme has three switch nodeterminals SW1 through SW3 which would typically be connected toswitching nodes such as nodes SW1 and SW2 as shown in FIG. 1 for currentsensing purposes to provide feedback control and sensing. A currentsensing summing node CSSUM combines current sensing signals frommultiple phases to measure the total power supply output current. Asecond series of switching nodes SWA through SWF are connected to theswitching nodes of a six-phase power supply that may be controlled bythe phase-doubling logic shown in FIG. 4. To provide current sensingfeedback for all six phases, pairs of resistors are arranged to formresistive dividers between the original switching nodes SW1-3 and thedoubled switching nodes SWA-F. For example, RA1 and RD1 form a dividerbetween SW1, SWA and SWD.

The embodiments of FIGS. 4 and 5 may provide a convenient and economicaltechnique for increasing the number of phases that may be controlled byan existing switching power supply controller. Existing “off-the-shelf”and/or custom controllers are complete designs that have been tested,evaluated and debugged for commercial use. A controller is typicallyfabricated on an integrated circuit (IC) chip that is usually eithermounted in a package on a printed circuit (PC) board or included as partof a multi-chip module. In accordance with the inventive principles ofthis patent disclosure, logic to generate a greater number of switchingcontrol signals (and/or provide feedback from an increased number ofphases) may be fabricated separate from the IC on which the controlleris formed. Such logic may, for example, be implemented with othercommonly available combinational and sequential logic IC chips andcomponents that are mounted in separate packages on the same PC board asthe controller. This may enable a switching power supply to be designedwith a greater number of phases using very few additional components andwithout having to redesign the entire controller IC. Thus, theperformance of an existing, commercially available switching powersupply controller may be substantially improved with only a nominalincrease in cost.

FIG. 6 illustrates a generalized embodiment of a switching power supplycontrol system according to the inventive principles of this patentdisclosure. FIG. 7 illustrates example waveforms of signals for theembodiment of FIG. 6. In this embodiment, a PWM signal is a digitalsignal from a switch mode power supply (SMPS) PWM controller. The outputQ of a D type flip-flop 38 is logic “1” at the beginning of a switchingsequence. As the PWM signal from a controller goes low at the end of itsfirst pulse, the falling edge of PWM triggers the D flip-flop causing alogic “0” in the Q output and a “1” in the Q# output. PWMi is the outputof the “AND” gate labeled Gate 1 which combines the signals Q and PWM.When Q is low, the second PWM pulse is unable to go through gate 1. PWMiignores the second PWM pulse. At the same time, PWMj, which is theoutput of AND Gate 2 (which combines the signals Q# and PWM) receivesthe second PWM pulse while Q# is “1”. As the D flip-flop receives thefalling edge of the second PWM pulse, its outputs switch to the oppositestates. The third PWM pulse is transferred to PWMi through Gate 1.Therefore, the PWM signal is split alternately to PWMi and PWMj.

A 2-1 multiplexer (MUX) including switches MUXi and MUXj transfers thecorresponding switch node signal signals SWi and SWj to SW as the PWMsignal toggles between PWMi and PWMj. For example, when the Q output ofthe D flip-flop is “1”, the PWM signal is transferred to PWMi, whereasthe SWi signal is switched to SW to provide the right phase switch nodesignal. The embodiment of FIG. 6 may be extended to implement any numberof phases, and the series of first PWM signals may be any number,including one.

FIG. 8 illustrates another example embodiment illustrating how fourcopies of the single phase doublers shown in FIG. 6 may be arranged toprovide four pairs of phases to implement an eight phase PWM controlleraccording to the inventive principles of this patent disclosure. In theembodiment of FIG. 8, a controller 40 has four PWM switching controloutputs PWM1-4. Each of these outputs is applied to a corresponding oneof four phase doubling blocks 42 through 48 which may be essentially thesame as the embodiment of FIG. 6. Each phase doubling block alternatelygenerates two switching control signals (for example, block 42 generatesPWMA and PWME in response to PWM1), and alternately applies one of twoswitching node signals to a corresponding one of the switching nodeterminals (e.g., SWA and SWE to SW1) of the controller 40.

FIG. 9 illustrates example waveforms for a PWM output and SW input forone pair of doubled phases in the embodiment of FIG. 8. FIG. 10illustrates example waveforms showing how all four of the controller PWMoutputs and all eight of the doubled PWM outputs may respond to a suddenload release. The output voltage V_(OUT) shows a slight overshoot as theload is released. This causes PWM4 to skip a pulse which may enable thePWMD and PWMH outputs to shift places relative to the other doubled PWMoutputs.

Since the embodiments described above can be modified in arrangement anddetail without departing from the inventive concepts, such changes andmodifications are considered to fall within the scope of the followingclaims.

1. A switching power supply control system comprising: an existingswitching power supply controller to generate a number of firstswitching control signals; and logic to generate a greater number ofsecond switching control signals in response to the first switchingcontrol signals.
 2. The system of claim 1 where the logic may generate:a first set of the second switching control signals in a first sequence;and a second set of the second switching control signals in a secondsequence.
 3. The system of claim 2 where the first and second sequencesare the same as a sequence for the first switching control signals. 4.The system of claim 2 where the logic may alternate between activatingthe first set and the second set.
 5. The system of claim 4 where thefirst and second sequences are the same as a sequence for the firstswitching control signals.
 6. The system of claim 1 where the logicincludes sequential logic to toggle one or more enable signals inresponse to one of the first switching control signals.
 7. The system ofclaim 6 where the logic includes a series of logic gates arranged totransmit each of the first switching control signals as one or more ofthe second switching control signals in response to the one or moreenable signals.
 8. The system of claim 1 further including a feedbacknetwork arranged to steer a number of second feedback signals to alesser number of first feedback signals.
 9. The system of claim 8 wherethe feedback network includes a first series of sensing elements coupledbetween a number of second switching nodes and a common sensing node.10. The system of claim 9 where the feedback network further includes asecond series of sensing elements coupled between the number of secondswitching nodes and a lesser number of first switching nodes.
 11. Thesystem of claim 10 where the first and second sensing elements arearranged to form dividers between the first switching nodes and secondswitching nodes.
 12. The system of claim 1 where the logic may steer anumber of second feedback signals to a lesser number of first feedbacksignals.
 13. The system of claim 12 where: each of the first feedbacksignals is coordinated with a corresponding one of the first switchingcontrol signals; and each of the second feedback signals is coordinatedwith a corresponding one of the second switching control signals. 14.The system of claim 12 where the logic includes switches to steer thefeedback signals.